1. Field of the Invention
The present invention relates to a direct-current power supply device that generates a power supply voltage for driving an LED, and more particularly to an effective technique utilized for a switching power supply device that generates a power supply voltage for driving a WLED (white light emitting diode), which is used for a backlight of a liquid crystal display monitor of a mobile device such as a portable phone, and for a semiconductor integrated circuit constituting the switching power supply device for driving power supply.
2. Description of Related Art
WLED is used as a backlight of a liquid crystal display panel of a mobile device such as a portable phone. A DC-DC converter including a boost switching regulator is commonly used in a power supply device that generates a power supply voltage for driving the WLED. Feedback control is performed in such a power supply device for driving an LED. In the feedback control, an LED drive current is converted into a voltage to feed back the voltage to a control circuit, the voltage is compared with a reference voltage by an error amplifier to generate a drive pulse having a pulse width corresponding to the voltage potential difference, and a switching element intermittently supplying a current to an inductor (coil) is driven in response to the drive pulse to keep the drive current constant. Such a power supply device for driving an LED is disclosed in Japanese Patent Application Laid-Open No. 2007-220855, for example.